PROJECT SUMMARY/ABSTRACT Developing effective therapies for patients with epithelial ovarian cancer (EOC) represents an unmet need. Pre-clinical data suggests a strong role for immunosurveillance as a mechanism of preventing recurrence in (EOC). Exploring the potential for a multi-antigen induced immune effector response to change outcome for patients is warranted. We seek to determine whether immune checkpoint blockade will augment multi-antigen vaccination to improve clinical outcomes in patients with EOC. We will begin by evaluating multi-antigen vaccination with WT-1 analog peptide and NY-ESO-1 overlapping peptide vaccine with POLY-ICLC (+ montanide) in the presence or absence of PD-1 blockade. Based on pre-clinical testing to be completed in project 1, we will then evaluate whether the addition of MUC16 OLP versus 55 mer will further enhance the efficacy of the combinatorial strategy of multi-antigen vaccination and checkpoint blockade. We postulate that antigen-specific immune responses, T cell activation/exhaustion, and immune suppression mechanisms including Treg and myeloid-derived suppressor cells (MDSCs) in blood and tumor tissue will be favorably modulated after vaccination and immunologic checkpoint blockade in EOC. We hypothesize that by analyzing broad antigen-specific responses and by characterizing the activated/exhausted T cells and immune suppressor cells, especially in tumor tissues, we will be able to understand the immunologic response in EOC patients and to define immunologic signatures predicting clinical response. Therefore, in our second aim, we will utilize comprehensive immune analysis to define antigen specific immune response (including epitope spreading to known and previously unrecognized antigens), T cell activation/exhaustion phenotype and tumor suppression mechanisms including regulatory T cells and myeloid derived suppressor cells in order to define optimal combinatorial approaches. Samples will be analyzed pre-immunization and post immunization +/- PD-1 blockade. By focusing on antigen discovery, we suggest that such efforts to determine the specificity and reactivity of autoantibodies occurring during ovarian cancer should help define a comprehensive repertoire of immune responses from the serum of cancer patients with diagnostic and/or prognostic value. Following the completion of the trials defining the safety and immunogenicity (Year 3), we will embark on a randomized phase II trial in the second and third remission setting using a multi-center approach. This parallels our previous work evaluating carbohydrate antigen based vaccines which were taken from the phase I setting to a multi valent construct with sufficient immunogenicity and safety data to warrant ongoing randomized testing to assess efficacy.